Optical interference tomographic image observing apparatus

ABSTRACT

An optical interference tomographic image observing apparatus is provided so as to detect the static or dynamic structure at a deep portion of a living body or the like and provide a multidimensional image thereof for observation. 
     The optical interference tomographic image observing apparatus includes a rotary prism apparatus which includes a Littrow reflector prism ( 1 ) having a 90-degree vertex and disposed near a circumference of a rotary body ( 4 ) in such a manner that a surface facing the vertex extends substantially perpendicular to a tangential line of the circumference, the prism having a characteristics such that when a light beam impinges the surface, the light beam is reflected in a direction parallel to the incidence direction. Through utilization of the characteristics, the reflection point can be scanned in a predetermined direction as the rotary body ( 4 ) rotates; and a delay reflection light beam is periodically generated when the rotary body rotates in the travel direction of the light beam and a progressive reflection light beam is periodically generated when the rotary body rotates in the opposite direction.

TECHNICAL FIELD

The present invention relates to a technique for detectingback-scattering light from a scattering potential which has a scatteringcenter at a micro object or the like located within, for example, aliving body, which is a medium that strongly scatters light; obtaininginformation regarding a scattering position and information regardingreflection amplitude by use of interference measurement means whichutilizes a phenomenon that coherence is present even in reflection lightfrom an object that strongly scatters light and which utilizes theshortness of coherence length of low-coherence light; and obtainingsingle-dimensional or two-dimensional image data, or multidimensionalimage data such as three-dimensional image data, while scanning theinterior of the object. More particularly, the present invention relatesto an optical interference tomographic image observing apparatus whichenables easy observation of a tomographic image of a light-scatteringmedium such as a living body by use of a remote device.

BACKGROUND ART

An attempt for obtaining a reflection tomographic image of a livingbody, which is a medium that strongly scatters light, starts fromconstruction of an interferometer by use of low-coherence light (seeNaohiro Tanno, “Kogaku” Vol. 28, No. 3, pp. 116-125 (1999)). Aconventional technique will be described with reference to FIGS. 1 and2.

FIG. 1 is a diagram showing the structure of a conventional light-wavereflection image measurement apparatus proposed by the presentinventors.

In this light-wave reflection image measurement apparatus, a light beamfrom a low-coherence (also referred to as partial-coherence) lightsource 71 is introduced directly to a Michelson's interferometer inorder to split the beam into two beams by means of a beam splitter 73.One of the split beams, which is to be used as reference light,undergoes frequency shift. The frequency-shifted light beam is reflectedby a movable reflection mirror 72, which also serves to change a depthposition within an object, and is caused to enter a photo detector 75.The other light beam or transmission light is supplied to an object 74to be measured as object irradiation light. The light isscatter-reflected by a layer of scattering objects located at a deepportion of the object 74 and having a different refraction index. Thereflection light, serving as object reflection light, is mixed with thereference light by means of the beam splitter 73 so as to causeinterference. As a result, a beat signal is detected by means of thephoto detector 75. While the positional relation between theillumination light and the object is changed in order to effectscanning, the detected electric signals are fed to a computer via afilter and an amplification/signal processing section, whereby thedetected electric signals are stored in the computer. The thus-storedelectric signals are converted to image data in order to obtain areflection tomographic image.

FIG. 2 is a diagram showing the structure of a conventionaltomographic-image observation apparatus which employs a structure on thebasis of the above-described principle and in which optical fibers aredisposed to form optical paths in order to cope with vibration andfacilitate handling (see, for example, Japanese Kohyo (PCT) PatentPublication No. 6-511312).

As shown in FIG. 2, a light beam from a light source 81 propagatesthrough a fiber 82 and enters a splitter/mixer circuit 86. One lightbeam emitted from the splitter/mixer circuit 86 propagates through afiber. Light coming out from the outgoing end of the fiber is convergedby means of a convex lens 83. As a result, the light is reflected by anobject 84, and the reflection light serves as object reflection light.After impartment of a frequency shift by means of a piezo-oscillationphase shifter 85, the other light beam emitted from the splitter/mixercircuit 86 is reflected by a movable reflection mirror 80, and thereflection light serves as reference light, which is mixed and is causedto interfere with the object reflection light by means of thesplitter/mixer circuit 86. The mixed light enters a photo detector 87,whereby a reflection tomographic image can be observed in the samemanner as described above.

Conventional interference measurement methods all utilize a movablereflection mirror for changing light reflection position (referencereflection position). In general, the movable reflection mirror is areflection mirror attached to a linear actuator or a galvano-motor.Since the linear actuator moves an object back and forth via gears, themoving speed is as low as several mm/sec. In another method, a longfiber is wound around an electrostrictive element such as an elementmade of PZT, and the length of a reflection light path is changedthrough extension and contraction of the fiber.

DISCLOSURE OF THE INVENTION

Among the above-described conventional methods, the method employing areflection mirror attached to a linear actuator or the like involvesproblems in that high-speed sweeping is difficult, and that when themirror is moved back and forth periodically, linearity is deteriorateddue to backlash and other causes.

Meanwhile, the method in which a long fiber is wound around anelectrostrictive element such as an element made of PZT and the lengthof a reflection light path is changed through extension and contractionof the fiber involves a problem in that since a path for reference lightbecomes excessively long, the temperature varies, and the length of apath for object light must be increased.

Furthermore, the apparatus utilizing a linear actuator and the apparatusutilizing an electrostrictive element are both large in size, andfabrication of a compact, transportable apparatus including aninterferometer is difficult.

Moreover, when sweeping speed is low, a very long time is needed tocomplete tomographic image measurement, which makes applying thetomographic image measurement to examination of a living body or amoving object difficult. In addition, when the path for reference lightand the path for reflection light are made excessively long, opticalsignals attenuate excessively. In this case, the SN ratio of an obtainedimage decreases, which makes observation of a deep portion of an objectdifficult.

In order to solve the above-described problems, the present inventionproposes a method and a specific apparatus which utilizes a rotatingLittrow reflector prism and which can reflect a light beam in order toproduce a delay reflection light beam or a progressive reflection lightbeam which travels toward the incoming direction of the light beam, evenwhen the reflection point moves along a circumference of a rotary bodyupon rotation thereof or a surface of the prism facing the vertexthereof inclines. The method and the apparatus utilize the features ofthe prism such that the prism reflects a light beam toward the directionfrom which the light beam comes, and even when the incoming light beaminclines with respect to the surface facing the 90-degree vertex, theprism accurately reflects a light beam toward the incoming direction.Further, the present invention realizes a reliable, high-speed-scanningreflection mirror by attaching prisms on a small, high-speed motor, andopens to the road to a compact, simplified, transportable apparatuswhich can be used practically for optical interference tomographic imageobservation, which is an object of the present invention. Moreover,another object of the present invention is to provide an opticalinterference tomographic image observing apparatus which extractsreflection signals of wide dynamic range and high SN ratio throughhigh-speed scanning in order to detect a static or dynamic structure ofa deep portion of, for example, a living body and to produce amultidimensional image for observation.

In order to achieve the above objects. the present invention providesthe following.

[1] An optical interference tomographic image observing apparatus,characterized by comprising a rotary prism apparatus which includes aLittrow reflector prism having a 90-degree vertex and disposed near acircumference of a rotary body in such a manner that a surface facingthe vertex extends substantially perpendicular to a tangential line ofthe circumference, the prism having a characteristics such that when alight beam impinges the surface, the light beam is reflected in adirection parallel to the incidence direction, wherein throughutilization of the characteristics, the reflection point can be scannedin a predetermined direction as the rotary body rotates; and a delayreflection light beam is periodically generated when the rotary bodyrotates in the travel direction of the light beam and a progressivereflection light beam is periodically generated when the rotary bodyrotates in the opposite direction.

[2] An optical interference tomographic image observing apparatus asdescribed in [1] above, further comprising:

means for splitting a light beam from a low-coherence light source intotwo light beams, one of the light beams, serving as reference light,being delayed or advanced by means of rotary scanning of the reflectionpoint in order to obtain a reflection light beam having a Doppler shiftfrequency, and the other light beam being converged to an object to bemeasured which has a multilayer structure in terms of refraction indexdistribution; an objective lens for capturing object reflection lightfrom a scattering potential portion at a deep portion of the multilayerobject; a photo detector for performing heterodyne detection forobtaining a beat signal of the shift frequency, which is generated onthe basis of the low coherence, characterized in that a maximuminterference signal can be obtained only when the reference light andthe object reflection light merge together after passage throughrespective optical paths having the same optical path length as measuredfrom the split point; means for calculating, in the form of coordinates,the scanned reflection point of the delay or progressive reflectionlight beam; and a signal control processing system, a computer, and adisplay which measure and display a reflection tomographic image, whileusing, as image data, the coordinates and an amplitude of the beatsignal representing reflection light from the scattering potential atthe deep portion of the object to be measured.

[3] An optical interference tomographic image observing apparatus asdescribed in [2] above, wherein the means for calculating, in the formof coordinates, the scanned reflection point of the reflection lightbeam includes a photo detector for capturing deflection angle reflectionlight from the rotary prism, wherein the photo detector generates atiming pulse upon detection of the deflection angle reflection lightbefore generation of the reflection light beam; and the scannedreflection point is calculated from the rotation frequency, rotationcircumferential length, and rotation angle of the rotary prism, and isused as a coordinate of the scattering potential.

[4] An optical interference tomographic image observing apparatus asdescribed in [2] above, wherein the travel direction of the light beamemitted from the low-coherence light source is referred to as a Z axis;a semi-transparent reflection mirror is provided as the means forsplitting the light beam into two beams; the objective lens is disposedin a direction toward which a light beam passing through thesemi-transparent reflection mirror travels, the light beam serving asobject irradiation light; a direction along which a reflection lightbeam from the semi-transparent reflection mirror serving as referencelight travels is referred to as a Y axis; the light source, thesemi-transparent reflection mirror, and the objective lens areintegrated into a unit structure; and a mechanism for rotating the unitstructure about the Y axis is provided in order to rotate the unitstructure to thereby sweep the irradiation point on the object to bemeasured along the X-axis direction, whereby observation of atwo-dimensional tomographic image on an X-Z plane is enabled.

[5] An optical interference tomographic image observing apparatus asdescribed in [2] above, wherein the respective means are accommodatedwithin a casing; a dielectric multilayer film reflection mirror whichreflects only the wavelength band of the low-coherence light source isdisposed before the photo detector in order to reflect and guide themixed-wave interference wave to the photo detector; a light source whosewavelength band differs from that of the low-coherence light source isprovided; a second half mirror is provided in order to reflect lightemitted from the second light source and cause the light to pass throughthe dielectric multilayer film reflection mirror, the half mirror, andthe objective lens in order to radiate the object to be measured,reflection light from the surface of the object traveling back along theabove-described optical path, and passing through the second halfmirror; a CCD camera is provided in the same casing in order to capturethe image of the surface having magnified by the objective lens; and adisplay is disposed outside the casing in order to enable previousobservation of a measurement position on the object.

[6] An optical interference tomographic image observing apparatus asdescribed in [5] above, wherein the casing is equipped with a griphandle which has a switch for starting acquisition of measurement dataof the tomographic image after positioning of the measurement pointthrough observation of the measurement point.

[7] An optical interference tomographic image observing apparatus asdescribed in [4] above, further comprising a rotation mechanism whichrotates about the X axis and which receives the casing on which the unitstructure is disposed at an angle of 90 degrees, whereby, in addition tothe observation of a two-dimensional tomographic image on an X-Z plane,scanning along the Y-axis direction is effected by the rotationmechanism in order to enable observation of a three-dimensionaltomographic image.

[8] An optical interference tomographic image observing apparatus asdescribed in [7] above, wherein the objective lens is replaced with anobjective lens for funduscopy; and the object irradiation light isscanned by use of a galvano-mirror.

[9] An optical interference tomographic image observing apparatus asdescribed in any one of [1] to [7] above, wherein the optical path forreference light is turned up and down by a group of reflection mirrorsin order to increase the length of the optical path; and an opticalfiber having a length corresponding to the increased length is disposedin the optical path extending between the half mirror for splitting andthe object, whereby remote measurement is enabled.

[10] An optical interference tomographic image observing apparatus asdescribed in any one of [1] to [7] above, wherein an optical fiber isdisposed in the optical path for reference light in order to increasethe length of the optical path; and an optical fiber capable oftransmitting images and having a length corresponding to the increasedlength is disposed in the optical path extending between the half mirrorfor splitting and the object, whereby remote measurement is enabled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram of a conventional light-wave reflectionimage measurement apparatus configured by use of a movable reflectionmirror.

FIG. 2 is a structural diagram of a conventional tomographic-imageobservation apparatus configured by use of optical fibers and a movablereflection mirror.

FIG. 3 is a structural diagram of a reflection-point scanning rotaryprism apparatus according to an embodiment of the present invention.

FIG. 4 is a diagram to be used for explaining light reflectioncharacteristics of a 45-degree right-angle prism of the reflection-pointscanning rotary prism apparatus according to the embodiment of thepresent invention.

FIG. 5 is a view showing an embodiment of an optical interferencetomographic image observing apparatus which includes thereflection-point scanning rotary prism apparatus according to thepresent invention.

FIG. 6 is a set of graphs showing waveforms of mixed wave interferencesignals.

FIG. 7 is a view showing another embodiment of the present inventionwhich is equipped with a mechanism for scanning along an X-axisdirection of an object to be measured.

FIG. 8 is a view showing another embodiment of the present invention inwhich a low-coherence light source, a half mirror, and an objective lensare connected to form a single unit.

FIG. 9 is a view showing an embodiment of a compact, portable,simplified apparatus according to the present invention.

FIG. 10 is a view showing an embodiment in which the apparatus of thepresent invention is applied to an ophthalmic examination apparatus.

FIG. 11 is a view showing an embodiment of an optical interferencetomographic image observing apparatus according to the present inventionequipped with an optical bundle fiber.

FIG. 12 is a view showing an embodiment of an optical interferencetomographic image observing apparatus according to the present inventionequipped with a galvano-mirror scanning mechanism.

FIG. 13 is a view showing an embodiment of an optical interferencetomographic image observing apparatus according to the present inventionequipped with a two-axis galvano-mirror scanning mechanism.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detail.

FIG. 3 is a structural diagram of a reflection-point scanning rotaryprism apparatus according to an embodiment of the present invention,wherein FIG. 3(a) is a top view of the apparatus, and FIG. 3(b) is aside view of the apparatus. FIG. 4 is a diagram to be used forexplaining light reflection characteristics of a 45-degree right-angleprism of the reflection-point scanning rotary prism apparatus, whereinFIG. 4(a) is an explanatory view showing reflection light in the case inwhich an incoming beam enters a diagonal surface perpendicularlythereto, and FIG. 4(b) is an explanatory view showing reflection lightin the case in which an incoming beam enters the diagonal surface notperpendicularly thereto, due to rotation of the prism.

As shown in these drawings, an incident light beam 2 from alow-coherence light source is caused to enter a rotary prism 1. As shownin FIG. 4, the rotary prism 1 is a Littrow reflector prism whose onevertex angle is 90 degrees and in which a reflection thin film 1 a of ametal, such as aluminum, which reflects light is vapor-deposited on thesides forming the 90-degree vertex. As shown in FIG. 3, in considerationof load balance, two or three prisms 1 are disposed on and fixed to arotary plate 4, serving as a rotary body, symmetrically with respect tothe axis of rotation. The rotary plate 4 is rotated by power of a motor3. FIG. 3 shows an example in which the rotary plate 4 rotates in thedirection indicated by φ.

First, light reflection characteristics of the Littrow reflector prismwill be described with reference to FIG. 4.

When a light beam U enters a diagonal surface BC perpendicularlythereto, as shown in FIG. 4(a), 45-degree incidence/reflection isrepeated at two sides (AB, AC) of the prism, and thereby producing areflection light beam U′, which travels toward the direction from whichthe light beam U comes. The position of the light beam U is determinedin such a manner that its cross section becomes symmetric with respectto a center line of the vertex. In this case, a left-hand half of thelight beam is reflected to the right side, and a right-hand half of thelight beam is reflected to the left side. Therefore, the light beam isreflected toward the incidence direction in such a manner that itsentire wave front becomes parallel to the diagonal surface.

Next, there will be considered a case in which the prism 1 has beenrotated by a rotation angle θi about the rotational axis O. In thiscase, internal reflection as shown in FIG. 4(b) occurs. Specifically,the light beam U enters the diagonal surface BC at an angle θi. When therefraction index of the prism glass is represented by n, the incidentangle θ_(o) to the side AB is represented by 45°−θr, where θr isdetermined by sin⁻¹(sinθi/n) in accordance with Snell's law. Since thereflection light beam traveling from the side AC forms the same anglewith respect to a line s shown in FIG. 4(b) as that formed by theincident light beam traveling to the side AB, the reflection light beamU′ becomes parallel to the incident light beam U in accordance withSnell's law. At this time, the reflection light beam is shifted to theright, depending on the rotation angle and the radius r of the lightbeam. In the present invention, the radius of the light beam is set to 6mm, and the reflection point scanning distance L is as small as about ±1mm. Therefore, when the turning radius OR is set to 7.5 mm, the rotationangle θi becomes about ±7.6 degrees. In this case, the amount of shiftof the axis of reflection light becomes about 10%. Since the amount ofshift is sufficiently small as compared to the diameter of the incidentlight beam, such a shift does not raise any problem in opticalinterference detection of the present invention. Various types ofLittrow reflector prisms are available; e.g., a 45-degree right-angleprism which has only two surfaces forming a 90-degree vertex, a cubecorner prism which has six such surfaces, and a prism which has aconical surface. The latter two prisms can reflect a light beam to adirection from which the light beam comes, regardless of whether thelight beam approaches the prism from the upper side, the lower side, theleft side, or the right side. The prism of the present embodimentprovides satisfactory delayed reflection light only when the entirecross section of the light beam is located within the diagonal surfaceBC of the prism. When the length of the side BC is 10 mm, thisrequirement is satisfied sufficiently within the above-describedrotational angle. As shown in the present embodiment, when therotational angle is set to 15.2 degrees, a desired reflection-pointscanning distance of 2 mm can be attained.

The present invention requires repeated scanning. When the rotationalspeed of the motor is set to, for example, 6,000 rpm, reflection lightcan be obtained at a frequency of 300 Hz through reflection by the threeprisms shown in FIG. 3, and thus, delay reflection light can begenerated at high frequency. The rotational speed of 6,000 rpm can berealized with ease by use of a commercially available small motor.Apparently, progressive reflection light can be generated when the prismapparatus is rotated in a direction opposite that shown in FIG. 3. Theprism apparatus can generate delay (progressive) reflection light at anarbitrary period through adjustment of the voltage of a motor powersupply 5.

FIG. 5 is a view showing an embodiment of an optical interferencetomographic image observing apparatus which includes the above-describedrotary prism apparatus.

As shown in FIG. 5, a low-coherence light source 6 is constituted by alight-emitting diode and a convex lens and emits substantially parallellight rays. The light source has a center wavelength λ of 0.88 μm and awavelength width Δλ of 40 nm and is estimated to have a spatialresolution ΔZ of 8.5 μm, as determined on the basis of the coherencelength. The emitted light beam is split into two beams by means of ahalf mirror 7. One light beam is reflected by means of a reflectionmirror 8 and enters the rotary prism 1 of the above-describedembodiment. Thus, the light beam is converted to delay reflection light2 at a predetermined position. The delay reflection light 2 travels backto the half mirror 7 as reference light.

The reflection light from the high speed rotary prism 1 has a Dopplershift frequency fb. For example, in the case of the above-describedembodiment, fb=10.6 MHz, as determined from the rotational angular speedof a circumferential point. Meanwhile, the other light beam ortransmission light passes through an objective lens 10 and reaches anobject 11 to be measured, which has a multi-layer structure, such as aliving body. Object reflection light from a deep portion of the objectis collected by the objective lens 10 and is caused to travel to thereflection mirror 8, at which the object reflection light is mixed withthe reference light so as to produce mixed-wave interference light. Themixed-wave interference light is reflected by means of a referencemirror 12 and is then reflected by means of a dielectric multi-layerfilm reflection mirror 13 capable of selectively reflecting light havinga wavelength of 0.88 μm (wavelength width: 40 nm) such that thereflection light propagates along a direction perpendicular to the sheetof FIG. 5. The reflection light is converged by means of a convex lens14 and is detected by a photo detector 15. When the electric field ofthe reference light is represented by Er and the electric field of theobject reflection light is represented by Es(x, y, z), due to thesquare-law detection action involved in photoelectric conversion, thephoto detector 15 outputs a signal represented by the followingexpression, including a heterodyne beat signal. $\begin{matrix}{{{I\left( {x,y,z} \right)} = {\frac{1}{2{\pi\Delta}\quad f}{\int_{- \infty}^{\infty}{{G(f)}{{E_{r} + {E_{s}\left( {x,y,z} \right)}}}^{2}\quad {f}}}}}\quad} \\{= {\lbrack{DCterms}\rbrack +}} \\{{E_{r}{E_{s}\left( {x,y,z} \right)}\sqrt{\frac{\pi}{\ln \quad 2}}{\cos \left( {2\pi \quad f_{b}t} \right)}\exp \left\{ {- {\frac{\pi^{2}}{\ln \quad 2}\left\lbrack {\Delta \quad {f\left( {\tau - {z/c}} \right)}} \right\rbrack}^{2}} \right\}}}\end{matrix}$

Here, Δf represents a frequency width of the light source; and G(f)represents its frequency distribution function, wherein the frequency isassumed to follow a Gaussian distribution. [DCterms] represents the DCcomponent serving as background noise. τ=(dr−ds)/c, where dr representsthe optical distance between the half mirror 7 and the reflectionposition of the rotary prism 1, ds represents an optical distance to areflection point on the surface of the object, and z represents thedistance between the surface of the object and a reflection position ata deep portion. Accordingly, τ represents a delay time produced by therotary prism 1 when the surface of the object used as a reference. FromExpression (1), it is understood that a sine wave of the beat frequencyfb is modulated by a Gaussian function, and that the position of a peakof the modulated wave represents a Z-axis coordinate of a deep portionof the object that reflects light, and the amplitude of the peakrepresents the scattering intensity of a scattering potential at areflection point. Reference numeral 19 denotes a wiring terminal; 20denotes wiring; and 60 denotes a casing.

FIG. 6 is a set of graphs showing waveforms of mixed-wave interferencesignals in relation to the present invention, wherein FIG. 6(a) showstiming pulses and a waveform of a beat signal in the case of astationary mirror, FIG. 6(b) shows a waveform of a beat signal showing adistribution of reflective objects in a deep layer of an object to bemeasured and setting of gate pulses for determining measurement points,and FIG. 6(c) shows an image signal which is obtained throughbeat-frequency filtering and representing the distribution of thereflective objects.

FIG. 6(a) shows timing pulses output from a photo diode 9 shown in FIG.5 and a Doppler beat signal observed when a stationary mirror is placedin place of the object. The timing pulses can be obtained by capturingreflection light from, for example, the metal reflection thin film 1 aof the side AB of the rotary prism, before the rotary prism receives thelight beam. The time between the pulses corresponding to the distancebetween the rotary prism. From this, the relative position of thestationary mirror can be calculated. Due to low-coherent time c/Δf (c:velocity of light) shown in Expression (1), the beat signal assumes apulse shape, which provides a resolution ΔZ in relation to the Z-axisdistance of the deep portion of the object. Within an object having arefraction index n, the resolution is represented by ΔZ/n. In a livingbody or the like, the resolution becomes about 6.5 μm. When the objecthas a multi-layer structure, a reflection signal as shown in FIG. 6(b)is observed. The incident light beam 2 is received by the rotary prism 1over a limited period of time. Therefore, a surface position of theobject is identified and a gate pulse is generated on the basis of thesurface position, and only the beat frequency is filtered. As a result,the waveform shown in FIG. 6(c) is obtained. When the position of theirradiation point on the object 11 to be measured is scanned for eachrotary prism, a signal can be obtained each of successive positions Xn,Xn+1, etc., along the X-axis. A pixel signal is produced for eachcombination of an Z-axis section having a length corresponding to thedistance of resolution and an X-axis section having a lengthcorresponding to the diameter of the focal point of the objective lens;e.g., 20 μm, and is then subjected to image processing. A computer 22performs control of the rotational speed of the prism, storage of data,and necessary computation processing via a control system 21. By virtueof these operations, the computer 22 can immediately display atwo-dimensional tomographic image on a display during observationthereof.

The present embodiment includes means for enabling a user tomicroscopically observe the surface of the object 11 via the objectivelens 10. Specifically, as shown in FIG. 5, a high-intensity lightemitting diode 16 is disposed at a predetermined position; and the lightemitted from the diode 16 is reflected by means of a half mirror 17 asshown in the drawing and is passed through the above-describeddielectric multi-layer film reflection mirror 13. At this time, thewavelength range of the light emitting diode 16 is selected so as tofall within a visible range. This visible light is reflected by means ofthe half mirror 7 so as to illuminate the surface of the object. As aresult, reflection light travels backward, passes through the halfmirror 17, and reaches a CCD camera 18. For example, when the objectivelens 10 has a focal distance f of 16 mm and the CCD camera 18 isequipped with a close-up lens, a microscopic image magnified some tensof times can be obtained. This magnified image is observed by use of acompact liquid-crystal display unit 23 or the like disposed separately.Since light emitted from the low-coherence light source 6 contains aslight amount of a red component, an irradiation point at which atomographic image is to be observed is also observed within a field ofview of the microscope. This method facilitates positioning within thefield of view.

Next, FIG. 7 shows another embodiment which is equipped with a mechanismfor scanning along the X-axis direction.

As shown in FIG. 7, a low-coherence light source 6, a half mirror 7′ (acube half mirror in this example), and an objective lens 10 are arrangedalong a straight line and are connected together to form a unitstructure 50. As shown in FIG. 7, the direction along which a reflectionlight beam and a mixed-wave interference light beam travel is referredto as a Y axis. The unit structure 50 is provided with a deflectionangle turning mechanism 51, which rotates the unit structure 50 aboutthe Y axis over an angle θ=±4.5 degrees. As a result, when the distancebetween the Y axis and the object is set to, for example, about 40 mm,as shown in FIG. 8, the irradiation point on the surface of the objectcan be changed along the X-axis direction by about ±3.0 mm. In anexample case in which the X-axis is divided into 300 sections inconsideration that the objective lens has a spatial resolution of 20 μmas measured on the irradiation surface, the 300 sections are scannedover one second when the rotary prism generates delay light at 300 Hz.As a result, a two-dimensional tomographic image can be converted toimage data within 1 second. In this case, since the irradiation surfacebecomes arcuate, a correction surface is calculated in advance beforeobtaining imaged data during subsequent image processing.

Next, FIG. 9 shows an embodiment of a compact, portable, simplifiedapparatus.

In the present embodiment, the control processing system 21, thecomputer 22, and the compact liquid-crystal display 23 shown in FIG. 5are disposed outside a casing 60′; and the above-described variouscomponents are accommodated in the casing 60′ so as to constitute anobservation head as shown in FIG. 9. The casing 60′ is equipped with ahandle 60 a for transport, and a switch SW for starting and stoppingdata acquisition after determination of a measurement point. Thus, theobservation head is made transportable. In this case, unlike the case ofFIG. 7, the above-described unit structure 50 a is rotated by 90 degreesin order to facilitate approach to an object to be measured. When a unitstructure 50 b oriented as shown in FIG. 9 is provided on the casing60′, the handle is provided as indicated by 60 b.

Next, FIG. 10 shows an embodiment in which the present apparatus isapplied to an ophthalmic examination apparatus.

As shown in FIG. 10, the objective lens 10 shown in FIG. 5 is replacedwith an objective lens 24 for funduscopy; a mechanism 24 a for movingthe lens 24 back and forth is provided; and an enclosure casing 60″ ismounted on a rotary table 26. The irradiation position at the eyegroundcan be changed freely by appropriately controlling the rotary table 26and the turning mechanism 51 shown in FIG. 7. The turning mechanism 51is provided to constitute a tomographic image observation head 90 forophthalmic use.

Next, FIG. 11 is a view showing an embodiment of an optical interferencetomographic image observing apparatus equipped with an optical bundlefiber, which is used as a probe for forming an optical path to an objectto be measured.

The optical path of FIG. 7 which extends from the objective lens 10 toan object to be measured is replaced with an optical bundle fiber 10 aas shown in FIG. 11. The optical bundle fiber 10 a guides irradiationlight emitted from the objective lens 10. For example, a GRIN lens(distributed index fiber-type lens) 10 b is attached to the tip end ofthe fiber in order to radiate light onto the object. Reflection lightfrom a deep portion of the object is collected by the lens and is causedto reach the photo detector 15, whereby a tomographic image is observedin the same manner as in the case of FIG. 7. In this case, the length ofthe optical path for reference light must be increased by the length ofthe fiber. Therefore, as shown in FIG. 11, a plurality of reflectionmirrors 8 a and 8 b, etc. are used in order to turn the path up and downsuch that the path attains a desired length. Needless to say, a similaroptical fiber may be disposed on the optical path for reference light.Moreover, it is apparent that the same observation is possible even whena distributed index fiber capable of transmitting images is used insteadof the optical bundle fiber 10 a (a bundle of fibers).

The present embodiment enables provision of endoscopes, microscopes,fiber catheters, and remote measurement in processes for fabricatingvarious materials.

FIG. 12 shows an embodiment of an optical interference tomographic imageobserving apparatus equipped with a galvano-mirror scanning mechanism.

As shown in FIG. 12, a galvano-mirror 8 c is provided in a path forobject irradiation light in order to change the traveling direction oflight radiated onto an object to be measured, to thereby sweep theirradiation point along the Y′ axis in FIG. 12, whereby a desiredtomographic image is obtained.

FIG. 13 shows an embodiment in which another galvano-mirror 8 d isdisposed in order to enable scanning along the X-axis direction, tothereby constitute an apparatus for examination of the eyeball.

As shown in FIG. 13, by virtue of scanning along two directions,radiation light can be swept freely. The simplified compact apparatuswhich utilizes the features of the embodiment shown in FIG. 5 can beused with ease at medical sites.

Although wiring is partially omitted in FIGS. 12 and 13, apparently, adrive power source and wiring therefor are necessary.

Even when any of the structures of the embodiments is employed, therecan be realized an optical interference tomographic image observingapparatus in which an object to be measured includes a dynamicscattering potential portion and generates object reflection lighthaving a Doppler shift frequency, characterized by comprising a computerwhich passes a Doppler shift beat component output from the photodetector for detecting the mixture inference light through an electricfilter and detects the Doppler shift beat component in order tosynthesize a plurality of spatial pixel component signals, to therebyextract information regarding the amplitude of light scattered from thedynamic scattering potential portion; calculates and displays, on thebasis of the frequency of the Doppler shift beat component, the movingspeed and direction of the dynamic scattering potential portion for eachthree-dimensional pixels of a depth reflection image and a verticalcross-sectional image; thereby enabling visualization of a dynamicstructure, such as blood flow distribution at a deep portion of a livingbody.

As described above, the present invention has the following features.

(1) There is provided a rotary prism which includes a Littrow reflectorprism having a 90-degree vertex and disposed at a circumferentialportion of a rotary body in such a manner that a surface facing thevertex extends substantially perpendicular to a tangential line of thecircumference. The prism has a characteristics such that when a lightbeam impinges the surface, the light beam is reflected in a directionparallel to the incidence direction. Through utilization of thecharacteristics, the reflection point can be scanned in a predetermineddirection as the rotary body rotates. A delay reflection light beam isperiodically generated when the rotary body rotates in the traveldirection of the light beam and a progressive reflection light beam isperiodically generated when the rotary body rotates in the oppositedirection. A means for splitting a light beam from a low-coherence lightsource into two light beams is provided. One of the light beams, servingas reference light, is delayed or advanced by means of rotary scanningof the reflection point in order to obtain a reflection light beamhaving a Doppler shift frequency. The other light beam is converged toan object to be observed which has a multilayer structure in terms ofrefraction index distribution. An objective lens is provided in order tocapture object reflection light from a scattering potential portion at adeep portion of the multilayer object. A photo detector for performingheterodyne detection is provided in order to obtain a beat signal of theshift frequency, which is generated on the basis of the low coherence,characterized in that a maximum interference signal can be obtained onlywhen the reference light and the object reflection light merge togetherafter passage through respective optical paths having the same opticalpath length as measured from the split point. A means for calculating,in the form of coordinates, the scanned reflection point of the delay orprogressive reflection light beam is provided. Further, a signal controlprocessing system, a computer, and a display are provided in order tomeasure and display a reflection tomographic image, while using, asimage data, the coordinates and an amplitude of the beat signalrepresenting reflection light from the scattering potential at the deepportion of the object to be measured. The means for calculating, in theform of coordinates, the scanned reflection point of reflection lightbeam includes a photo detector for capturing deflection angle reflectionlight from the rotary prism, wherein the photo detector generates atiming pulse upon detection of the deflection angle reflection lightbefore generation of the reflection light beam; and the scannedreflection point is calculated from the rotation frequency, rotationcircumferential length, and rotation angle of the rotary prism, and isused as a coordinate of the scattering potential. Thus, an opticalreflection tomographic image can be observed.

Moreover, the travel direction of the light beam emitted from thelow-coherence light source is referred to as a Z axis; asemi-transparent reflection mirror is provided as the means forsplitting the light beam into two beams; the objective lens is disposedin a direction toward which a light beam passing through thesemi-transparent reflection mirror travels, the light beam serving asobject irradiation light; a direction along which a reflection lightbeam from the semi-transparent reflection mirror serving as referencelight travels is referred to as a Y axis; the light source, thesemi-transparent reflection mirror, and the objective lens areintegrated into a unit structure; and a mechanism for rotating the unitstructure about the Y axis is provided in order to rotate the unitstructure to thereby sweep the irradiation point on the object to bemeasured along the X-axis direction, whereby observation of atwo-dimensional tomographic image on an X-Z plane is enabled. Therespective means described in claim 2 are accommodated within a casing;a dielectric multilayer film reflection mirror which reflects only thewavelength band of the low-coherence light source is disposed before thephoto detector in order to reflect and guide the mixed-wave interferencewave to the photo detector; a light source whose wavelength band differsfrom that of the low-coherence light source is provided; a second halfmirror is provided in order to reflect light emitted from the secondlight source and cause the light to pass through the dielectricmultilayer film reflection mirror, the half mirror, and the objectivelens in order to radiate the object to be measured, reflection lightfrom the surface of the object traveling back along the above-describedoptical path, and passing through the second half mirror; a CCD camerais provided in the same casing in order to capture the image of thesurface having magnified by the objective lens; and a display isdisposed outside the casing in order to enable previous observation of ameasurement position on the object. The casing described in claim 5 isequipped with a grip handle which has a switch for starting acquisitionof measurement data of the tomographic image after positioning of themeasurement point through observation of the measurement point. Theoptical interference tomographic image observing apparatus furthercomprises a rotation mechanism which rotates about the X axis and whichreceives the casing on which the unit structure is disposed at an angleof 90 degrees, whereby, in addition to the observation of atwo-dimensional tomographic image on an X-Z plane, scanning along theY-axis direction is effected by the rotation mechanism in order toenable observation of a three-dimensional tomographic image. Theobjective lens is replaced with an objective lens for funduscopy; therotation mechanism described in claim 7 is provided; and thus agalvano-mirror scanning apparatus for ophthalmic measurement isprovided. In the above-described apparatus, the optical path forreference light is turned up and down by use of a group of reflectionmirror by a group of reflection mirrors in order to increase the lengthof the optical path; and an optical fiber having a length correspondingto the increased length is disposed in the optical path extendingbetween the half mirror for splitting and the object, whereby remotemeasurement is enabled. Alternatively, a fiber bundle or distributedindex optical fiber, which can transmit images and has a lengthcorresponding to the increased length is disposed in the optical pathextending between the half mirror for splitting and the object, wherebyremote measurement is enabled.

In order to increase operation speed, the optical interferencetomographic image observing apparatus is provided with a computerdisplay which detects conditions of a deep portion of an object to bemeasured over a desired area; and which records and stores areproduction signal of each pixel, performs signal processing therefor,and displays the processed signal as a multidimensional deep-portiontomographic image.

The respective structures of the above-described embodiments may bemodified without departing from the spirit of the present invention, andsuch modifications fall within the scope of the present invention.

The present invention is not limited to the above-described embodiments.Numerous modifications and variations of the present invention arepossible in light of the spirit of the present invention, and they arenot excluded from the scope of the present invention.

As have been described in detail, the present invention achieves thefollowing effects.

(A) There are provided a method and a specific apparatus which utilizesa rotating Littrow reflector prism which can reflect a light beam inorder to produce a delay reflection light beam or a progressivereflection light beam which travels toward the incoming direction of thelight beam, even when the reflection point moves along a circumferenceof a rotary body upon rotation thereof or a surface of the prism facingthe vertex thereof inclines. The method and the apparatus utilize thefeatures of the prism such that the prism reflects a light beam towardthe direction from which the light beam comes, and even when theincoming light beam inclines with respect to the surface facing the90-degree vertex, the prism accurately reflects a light beam toward theincoming direction. Moreover, a reliable, high-speed-scanning reflectionmirror can be realized by attaching prisms on a small, high-speed motor;and such a reflection mirror opens to the road to a compact, simplified,transportable apparatus which can be used practically for opticalinterference tomographic image observation.

(B) Moreover, reflection signals having a wide dynamic range and a highSN ratio can be extracted through high-speed scanning in order to detecta static or dynamic structure of a deep portion of, for example, aliving body and to produce a multidimensional image. Thus, morphologicalinformation, medical information such as blood flow distribution, andstructural information of various materials such as semiconductormaterials, etc. can be observed in a non-invasive or non-destructivemanner at high spatial resolution of a microscopic level. In addition, anovel, transportable, compact optical interference tomographic imageobserving apparatus can be provided. Moreover, the present invention isexpected to create a new industry for practical apparatuses which can beused for various non-destructive material inspections and variousnon-invasive inspections for living bodies in relation to dermatology,cosmetic dermatology, and dentistry.

INDUSTRIAL APPLICABILITY

The optical interference tomographic image observing apparatus accordingto the present invention can detect a static or dynamic structure of adeep portion of, for example, a living body and to produce amultidimensional image. Thus, morphological information, medicalinformation such as blood flow distribution, and structural informationof various materials such as semiconductor materials, etc. can beobserved in a non-invasive or non-destructive manner at high spatialresolution of a microscopic level. In particular, the opticalinterference tomographic image observing apparatus according to thepresent invention is suitable for various non-destructive materialinspections and various non-invasive inspections for living bodies inrelation to dermatology, cosmetic dermatology, and dentistry.

What is claimed is:
 1. An optical interference tomographic imageobserving apparatus, characterized by comprising a rotary prismapparatus which includes a Littrow reflector prism having a 90-degreevertex and disposed near a circumference of a rotary body in such amanner that a surface facing the vertex extends substantiallyperpendicular to a tangential line of the circumference, the prismhaving a characteristics such that when a light beam impinges thesurface, the light beam is reflected in a direction parallel to theincidence direction, wherein through utilization of the characteristics,the reflection point can be scanned in a predetermined direction as therotary body rotates; and a delay reflection light beam is periodicallygenerated when the rotary body rotates in the travel direction of thelight beam and a progressive reflection light beam is periodicallygenerated when the rotary body rotates in the opposite direction,wherein the optical interference tomographic image observing apparatusfurther comprises: means for splitting a light beam from a low-coherencelight source into two light beams, one of the light beams, serving asreference light, being delayed or advanced by means of rotary scanningof the reflection point in order to obtain a reflection light beamhaving a Doppler shift frequency, and the other light beam beingconverged to an object to be measured which has a multilayer structurein terms of refraction index distribution; an objective lens forcapturing object reflection light from a scattering potential portion ata deep portion of the multilayer object; a photo detector for performingheterodyne detection for obtaining a beat signal of the shift frequency,which is generated on the basis of the low coherence, characterized inthat a maximum interference signal can be obtained only when thereference light and the object reflection light merge together afterpassage through respective optical paths having the same optical pathlength as measured from the split point; means for calculating, in theform of coordinates, the scanned reflection point of the delay orprogressive reflection light beam; and a signal control processingsystem, a computer, and a display which measure and display a reflectiontomographic image, while using, as image data, the coordinates and anamplitude of the beat signal representing reflection light from thescattering potential at the deep portion of the object to be measured.2. An optical interference tomographic image observing apparatus asdescribed in claim 1, wherein the means for calculating, in the form ofcoordinates, the scanned reflection point of the reflection light beamincludes a photo detector for capturing deflection angle reflectionlight from the rotary prism, wherein the photo detector generates atiming pulse upon detection of the deflection angle reflection lightbefore generation of the reflection light beam; and the scannedreflection point is calculated from the rotation frequency, rotationcircumferential length, and rotation angle of the rotary prism, and isused as a coordinate of the scattering potential.
 3. An opticalinterference tomographic image observing apparatus as described in claim1, wherein the travel direction of the light beam emitted from thelow-coherence light source is referred to as a Z axis; asemi-transparent reflection mirror is provided as the means forsplitting the light beam into two beams; the objective lens is disposedin a direction toward which a light beam passing through thesemi-transparent reflection mirror travels, the light beam serving asobject irradiation light; a direction along which a reflection lightbeam from the semi-transparent reflection mirror serving as referencelight travels is referred to as a Y axis; the light source, thesemi-transparent reflection mirror, and the objective lens areintegrated into a unit structure; and a mechanism for rotating the unitstructure about the Y axis is provided in order to rotate the unitstructure to thereby sweep the irradiation point on the object to bemeasured along the X-axis direction, whereby observation of atwo-dimensional tomographic image on an X-Z plane is enabled.
 4. Anoptical interference tomographic image observing apparatus as describedin claim 1, wherein the respective means are accommodated within acasing; a dielectric multilayer film reflection mirror which reflectsonly the wavelength band of the low-coherence light source is disposedbefore the photo detector in order to reflect and guide the mixed-waveinterference wave to the photo detector; a light source whose wavelengthband differs from that of the low-coherence light source is provided; asecond half mirror is provided in order to reflect light emitted fromthe second light source and cause the light to pass through thedielectric multilayer film reflection mirror, the half mirror, and theobjective lens in order to radiate the object to be measured, reflectionlight from the surface of the object traveling back along theabove-described optical path, and passing through the second halfmirror; a CCD camera is provided in the same casing in order to capturethe image of the surface having magnified by the objective lens; and adisplay is disposed outside the casing in order to enable previousobservation of a measurement position on the object.
 5. An opticalinterference tomographic image observing apparatus as described in claim4, wherein the casing is equipped with a grip handle which has a switchfor starting acquisition of measurement data of the tomographic imageafter positioning of the measurement point through observation of themeasurement point.
 6. An optical interference tomographic imageobserving apparatus as described in claim 3, further comprising arotation mechanism which rotates about the X axis and which receives thecasing on which the unit structure is disposed at an angle of 90degrees, whereby, in addition to the observation of a two-dimensionaltomographic image on an X-Z plane, scanning along the Y-axis directionis effected by the rotation mechanism in order to enable observation ofa three-dimensional tomographic image.
 7. An optical interferencetomographic image observing apparatus as described in claim 6, whereinthe objective lens is replaced with an objective lens for funduscopy;and the object irradiation light is scanned by use of a galvano-mirror.8. An optical interference tomographic image observing apparatus asdescribed in any one of claims 1 to 6, wherein the optical path forreference light is turned up and down by a group of reflection mirrorsin order to increase the length of the optical path; and an opticalfiber having a length corresponding to the increased length is disposedin the optical path extending between the half mirror for splitting andthe object, whereby remote measurement is enabled.
 9. An opticalinterference tomographic image observing apparatus as described in anyone of claims 1 to 6, wherein an optical fiber is disposed in theoptical path for reference light in order to increase the length of theoptical path; and an optical fiber capable of transmitting images andhaving a length corresponding to the increased length is disposed in theoptical path extending between the half mirror for splitting and theobject, whereby remote measurement is enabled.